1. Technical Field
The present invention relates to a manufacturing method of a progressive refractive lens, and particularly relates to the manufacturing method of a progressive refractive lens configured to select a semi-finish lens based on a base curve and apply processing to the semi-finish lens.
2. Description of Related Art
At present, in a field of a spectacle lens, various types of the spectacle lenses have been developed according to a request of a wearer, so as to respond to myopia and hyperopia. A progressive refractive lens can be given as one of such developed spectacle lenses. The progressive refractive lens has a far vision part for viewing a far vision and a near vision part for viewing a near vision. Therefore, by wearing the progressive refractive lens, the wearer can visually recognize a field from a far scenery to an object within an arm reach. Further, a progressive part for viewing an intermediate vision is provided between the far vision part and the near vision part. In this progressive part, diopter is continuously varied. Therefore, when a visual line is moved between the far vision and the near vision, move of the visual line with less strange feeling can be realized.
Similarly to a normal spectacle lens, the progressive refractive lens has a first surface being an object side surface, and a second surface being an eyeball side surface. Then, the progressive refractive lens having the progressive surface on the first surface, is called “an outer surface progressive lens”. Also, the progressive refractive lens having the progressive surface on the second surface, is called “an inner surface progressive lens”. Explanation is given hereafter using the spectacle lens with the first surface formed as a convex surface, and the second surface formed as a concave surface, if not being described otherwise.
The outer surface progressive lens described in patent document 1 for example, is known.
Patent document 1 describes a technique of applying a free-form processing to a surface opposed to the second surface of a semi-finish lens having a previously completed second surface (concave surface), and forming the first surface (convex surface) having a progressive refractive power. The progressive refractive power is also called a “progressive surface” hereafter.
The inner surface progressive lens described in patent documents 2 and 3 for example, is known.
As shown in line 41 to line 43 from the top of page 4 and FIG. 1, patent document 2 describes a technique of suppressing a fluctuation of a base curve showing a basic refractive power of the first surface (convex surface) by forming the progressive surface on the second surface (concave surface).
Also, patent document 3 describes the following content as a subject in a conventional art.
The inner surface progressive lens having a large addition power has a shape largely deviated from an approximately spherical shape in such a manner that a curve becomes shallow on the second surface (concave surface), thus deteriorating a wearing feeling. Further, even in a case of the inner surface progressive lens having the large addition power, the base curve on the first surface (convex surface) is set to be small. In this case, a curvature difference needs to be generated between the first surface and the second surface, so as to satisfy a condition that the addition power is large. Therefore, the convex shape (namely “rear convex”) needs to be formed on the second surface (concave surface).
As the means for solving such a subject, patent document 3 describes a method of determining the base curve of the semi-finish lens, according to the addition power requested for the inner surface progressive lens. This base curve is the base curve of the first surface (convex surface) finally. According to patent document 3, as shown in table 1 and table 2 of the patent document 3, a table showing a value of an optical base curve is uniquely prepared, according to the spherical power requested for the first surface, and the addition power requested for the inner progressive lens. For example, as described in paragraph 0019 of patent document 3, a deep base curve (C-section in table 1) is set for the semi-finish lens corresponding to the addition power, although a shallow base curve (A-section in table 1) needs to be set originally. Thus, generation of the “rear convex” is avoided.